ABSTRAKT

To improve gas turbine performance, the operating temperature has been increased continuously. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Cooling methods are, therefore, much needed for the turbine blades to ensure long durability and safe operation. The blade tip region is exposed to hot gas flow, and is difficult to cool. A common way to cool the tip is to use serpentine passages with 180-degree turns under the blade tip-cap, taking advantage of the three-dimensional (3D) turning effect and impingement. Increased internal convective cooling is, however, required to increase the blade tip life. In this paper, augmented heat transfer of a blade tip with internal pin fins has been investigated numerically using a conjugated heat transfer approach. The computational models consist of two-pass channels with 180-degree turns and pin-fin arrays mounted on the internal tip caps. The computational domain includes the fluid region and the solid pins as well as the solid tip regions. Turbulent convective heat transfer between the fluid and pins, and heat conduction within the pins and tip are simultaneously computed. The inlet Reynolds number ranges from 100,000 to 600,000. Details of the 3D fluid flow and heat transfer over the tip-walls are presented. A comparison of the overall performance of the models is presented. It was found that due to the combination of turning impingement and pin-fin crossflow, the heat transfer coefficient of the pin-finned tip is about three times higher than that of a smooth tip. This augmentation is achieved at the cost of a pressure drop penalty of 7%. With the conjugated heat transfer method, not only the simulated model is close to the experimental model, but also the distribution of the external tip heat transfer and pin-fin surface heat flux can be used in the thermal design of blade tips.